1. Field of the Invention
The present invention relates to a method of treating calcium nitrate formed by the process of contacting a gas containing nitrogen oxides with a calcium-containing absorption liquid to absorb and remove the nitrogen oxides.
When the nitrogen oxides contained in the exhaust gases are removed by absorption therefrom by the conventional wet denitration process, calcium nitrate is formed in the denitration waste liquid. However, no satisfactory method of disposing calcium nitrate solution has been developed and there remains the possibility that a novel pollution problem will arise if the thus formed calcium nitrate is disposed of in an improper manner.
2. Description of the Prior Art
In recent years, nitrogen oxides have drawn public attention because they cause air pollution problems as exemplified by the formation of photochemically derived oxidants. A number of dry and wet denitration methods for removing nitrogen oxides from exhaust gases have been proposed. In the conventional wet denitration method, the nitrogen oxides in the exhaust gases discharged from a boiler, incineration furnace, coke oven or the like are captured by absorbing and oxidizing them in an absorption liquid. However, treatment or disposal of the liquid which results from the denitration operation has not yet been sufficiently investigated and there are risks of causing new types of secondary or tertiary pollution problems if the wasteliquid is disposed of in an improper manner.